public class j1405 {
    public static void main(String[] args) {
        double sum = 0;
        for(int i = 1;i <= 100;i++){
            if(i % 2 == 0){
                sum -=(1.0/i);
            }
            else{
                sum += (1.0/i);
            }
        }
        System.out.println(sum);
    }
}
